fix(gateway): isolate deferred platform imports from os.environ leaks

microsoft-teams-apps calls load_dotenv(find_dotenv(usecwd=True)) at import time, which can pull a root-profile .env into every gateway process during plugin_entries() discovery and break profile secret isolation.

Snapshot/restore os.environ around deferred loaders, and honor explicit api_server enabled:false the same way _enable_from_env does for other platforms.

Fixes #62935

gateway/platform_registry.py

@@ -29,12 +29,36 @@ Usage (gateway side):
 """
 
 import logging
+import os
+from contextlib import contextmanager
 from dataclasses import dataclass, field
-from typing import Any, Awaitable, Callable, Optional
+from typing import Any, Awaitable, Callable, Iterator, Optional
 
 logger = logging.getLogger(__name__)
 
 
+@contextmanager
+def _isolated_os_environ() -> Iterator[None]:
+    """Snapshot and restore ``os.environ`` around a deferred platform import.
+
+    Some third-party SDKs (notably ``microsoft-teams-apps``) call
+    ``load_dotenv(find_dotenv(usecwd=True))`` at module import time. That
+    walks up from the process cwd and mutates the process-global environ —
+    leaking root-profile secrets into secondary profiles and bypassing
+    Hermes's own dotenv / secret-scope rules (#62935).
+
+    Deferred loaders are import-and-register only; any environ mutation they
+    cause is treated as an unwanted side effect and discarded.
+    """
+    saved = dict(os.environ)
+    try:
+        yield
+    finally:
+        os.environ.clear()
+        os.environ.update(saved)
+
+
+
 @dataclass
 class PlatformEntry:
     """Metadata and factory for a single platform adapter."""
@@ -205,7 +229,10 @@ class PlatformRegistry:
         if loader is None:
             return
         try:
-            loader()
+            # Isolate environ so import-time dotenv / env mutation cannot leak
+            # across profiles or override explicit YAML disables (#62935).
+            with _isolated_os_environ():
+                loader()
         except Exception as e:
             logger.warning(
                 "Deferred load of platform '%s' failed: %s",

tests/gateway/test_platform_registry.py

@@ -494,3 +494,41 @@ class TestPluginEnablementGate:
                 )
         finally:
             _reg.unregister("myrejectedplat")
+
+
+
+class TestDeferredLoadEnvironIsolation:
+    """Deferred platform imports must not leak os.environ mutations (#62935)."""
+
+    def test_deferred_loader_environ_mutations_are_discarded(self, monkeypatch):
+        monkeypatch.delenv("API_SERVER_ENABLED", raising=False)
+        monkeypatch.delenv("LEAKED_FROM_IMPORT", raising=False)
+        assert "API_SERVER_ENABLED" not in os.environ
+
+        reg = PlatformRegistry()
+
+        def _polluting_loader():
+            os.environ["API_SERVER_ENABLED"] = "true"
+            os.environ["LEAKED_FROM_IMPORT"] = "1"
+            entry, _ = TestPlatformRegistry()._make_entry("polluter")
+            reg.register(entry)
+
+        reg.register_deferred("polluter", _polluting_loader)
+        assert reg.get("polluter") is not None
+        assert "API_SERVER_ENABLED" not in os.environ
+        assert "LEAKED_FROM_IMPORT" not in os.environ
+
+    def test_deferred_loader_preserves_preexisting_environ(self, monkeypatch):
+        monkeypatch.setenv("HERMES_KEEP", "alive")
+        reg = PlatformRegistry()
+
+        def _loader():
+            os.environ["HERMES_KEEP"] = "clobbered"
+            os.environ["TEMP_LEAK"] = "1"
+            entry, _ = TestPlatformRegistry()._make_entry("keeper")
+            reg.register(entry)
+
+        reg.register_deferred("keeper", _loader)
+        assert reg.get("keeper") is not None
+        assert os.environ.get("HERMES_KEEP") == "alive"
+        assert "TEMP_LEAK" not in os.environ